Comparação entre as técnicas de exame a fresco, histopatologia e PCR, no diagnóstico da hepatopancreatite necrosante (NHP), no camarão Litopenaeus vannamei

Abstract

In Brazil, the culture of Pacific white shrimp Litopenaeus vannamei achieves better results in the northeast region due to its tropical climate, suitable water quality and the existence of estuarine areas suitable for penaeid culture. However, Brazilian shrimp farming has developed rapidly and disorderly, favoring the outbreak of epizootics from varied etiologies. The Necrotizing Hepatopancreatitis is a disease caused by an intracellular bacterium from the Rickettsia order (NHPB), which stands out among shrimp bacterial epizootics responsible for high mortalities and economical losses due to its difficult control and diagnosis. In the light of this, the aim of this work is to compare two traditional techniques, the wet-mount and histopathology analyses, with a molecular method, the Polimerase Chain Reaction (PCR), for the diagnosis of NHPB in L. vannamei. One hundred and fifty four intermolt shrimp were collected from grow-out ponds of a farm located in the south of Rio Grande do Norte State/Brazil. The hepatopancreas of each animal was divided into three parts, being one readily wet-mounted and examined under a light microscope and the other two fixed and preserved for later histopathology and PCR analyses. The parameters observed in wet-mount analysis were color, amount of lipids, deformation of tubules, loosen cells and melanization; while parameters observed in histopathology were hemocytic infiltration, edema, granulomatous lesions and atrophy of tubules. PCR positive animals presented mean lower lipid levels, mean higher score for deformation of tubules and a higher percentage of individuals presenting hepatopancreatic lesions (loosen cells, melanization, hemocytic infiltration, granulomatous lesions and tubules atrophy) than PCR negative animals. No significant relation (P≥0,05) was found among PCR results and those parameters observed in wet-mount or histopathology. A significant percentage of PCR negative individuals also presented hepatopancreatic lesions and abnormalities, possibly related to other etiology rather than NHPB. This work concludes that no significant relation among wet-mount, histopathology and PCR techniques to diagnose NHPB can be assumed; therefore, neither wet-mount examination nor histopathology should be used alone as diagnostic techniques for this disease.